The present invention relates to Internet Protocol (IP) multimedia sessions, and more specifically to methods and systems of building IP multimedia sessions without the use of a central server.
The transmission of multimedia signals such as voice and video through IP is becoming increasingly common. Typically, in order to transmit multimedia signals, an IP multimedia session must be established. There are many public or private protocols for building IP multimedia sessions, e.g., Session Initiation Protocol (SIP) and the like. IP Multimedia Subsystem (IMS) is a network structure defined by the 3rd Generation Partnership Project (3GPP) that uses SIP to build multimedia sessions. A terminal device can use IP for transmitting multimedia information such as voice, image, video etc. through the IMS. Specific applications thereof may include telephone conferences and video conferences.
The building of a traditional IP multimedia session depends on a central server (e.g. an IMS system) that includes a central application server and a central media server. The application server is used for building the IP multimedia session (e.g., building a session according to the SIP) and for controlling service logic of the session. The media server is used for transmitting and processing actual multimedia signals. The advantage of the IP multimedia session depending on the central server is that it can support public or private session protocols and process complex service logic, and that the interface defined thereby is also consistent with the Internet Engineering Task Force (IETF) Internet standard. However, the building and maintaining of IP multimedia sessions that are dependent on the central server has a disadvantage of high dependence on the central server, and thus, the central server side has a relatively high computing pressure and the computing capability of the terminal device may not be sufficiently utilized. For example, if a small percentage of employees of an enterprise living in the same city want to have a telephone conference, they have to build an IP multimedia session by means of a remote central server of the enterprise located abroad, thereby causing excessive remote transmissions.
Another way to build IP multimedia session is to build IP multimedia sessions by using protocols such as SIP under a point-to-point (P2P) transmission environment (e.g., P2P-SIP). This has the advantage of zero dependency on any central server but has disadvantages that include: due to the P2P transmission specification, there exist no terminals having an application server or media server function under the built IP multimedia session environment; any one of the “points” is connected with other points in an one-to-one relation, so that device discovering, session building, coordinating and controlling processes are very complex; only simple voice or video communication can be supported; and complicated service logic cannot be supported as in the traditional IP multimedia session.